Re: Kernel panic at Ubuntu: IMA + Apparmor

[Al Viro <viro@ZenIV.linux.org.uk>]

On Fri, Apr 25, 2014 at 01:45:17PM -0700, Eric W. Biederman wrote:

> IMA-appraisal is fundamentally broken because I can take a mandatory
> file lock and prevent IMA-apprasial.
> 
> Using kernel_read is what allows this.
> 
> > Isn't it a clear motivating case???
> 
> kernel_read is not appropriate for IMA use.  The rest of this is just
> the messenger.
> 
> IMA needs to use a cousin of kernel_read that operates at a lower level
> than vfs_read.  A function that all of the permission checks and the
> fsnotify work.

It's worse than that, actually ;-/  IMA hooks in __fput() have interesting
interplay with revoke-related stuff as well.  Another very messy thing in
the same area is that it actually does ->read() from under ->i_mutex, leading
to all kinds of interesting locking issues...

I doubt that your "let's open-code vfs_read() guts" would be a good idea;
if nothing else, it might make more sense to make rw_verify_area() skip
the mandlock and security theatre when called in such situation.

What a mess... ;-/